The invention relates generally to cutting apertures in the lining material of lined conduits, such as for reestablishing side connections of a pipeline to lateral pipes, and more particularly to a method and apparatus for forming those apertures in an automated manner.
Conduits for water, sewage and other liquids frequently require repair because of leakage and various types of other structural failure. The leakage may be due to aging, cracking or corrosion. A common way to repair the existing pipeline is to uncover and remove the existing pipeline, replace it, then reconnect the new pipeline to the various lateral pipes emptying into the pipeline.
It is becoming common to repair aging pipelines with what is referred to as trenchless technology. A structurally independent replacement pipe is installed within the existing pipeline by pushing or pulling it through the pipeline without uncovering or removing the aged pipeline. Such processes are described in U.S. Pat. Nos. 4,009,063, 4,064,211 and 4,867,921, the contents of which are incorporated herein by reference. It is also becoming common to install nonstructural linings within existing pipelines to protect the existing pipelines from corrosion. For example, thin polymer tubes can be installed within existing pipelines that are exposed to corrosive fluids and thereby extend the life of the existing pipelines. This can be a highly cost effective approach, compared to the complete replacement of a pipeline system.
A drawback to this "pipe-within-a-pipe" technology is that after the liner (or replacement pipe) has been installed, it will cover openings in the existing pipeline which act as side or branch connections to lateral pipes. Laterals are smaller pipes of typically 4 to 6 inches in diameter. For example, a sewer line might run along a street and lateral lines will run from homes to feed sewage into the main line. These lateral connections must be reestablished after the existing pipeline is lined so that the existing pipeline can function as it did prior to the repair operation. This entails locating the lateral connections and cutting an opening in the liner to reestablish the lateral connection ("porting the lateral").
A conventional way of reestablishing the lateral connections by porting the laterals is described in U.S. Pat. Nos. 4,648,454 and 4,577,388, the contents of which are incorporated herein by reference. A sled containing a video camera and a cutting device is pulled through the re-lined pipeline. If the liner is of appropriate construction and is installed under appropriate conditions, the location of the lateral connections will appear as dimples on the inside wall of the replacement pipe and can be detected visually. Otherwise, the location of the lateral connection can be determined prior to installation of the liner or by various other methods that are well known in the art. Once the lateral connection opening is located, an operator will control the cutting with a mechanical cutter from the inside of the lined pipe to the lateral pipe by viewing a remote video image of the cutting operation and re-establishing the connection.
It also has been proposed to employ a water cutting system for opening lateral connections. As in the case of a mechanical cutting blade, a water cutting system projects a high pressure water stream from the inside of the conduit against the pipe wall to open the lateral connection. Optionally, abrasive material is dispersed in the water. A slightly oval shape can be achieved by moving the water jet from side to side. This system has not been widely accepted for commercial uses, due in part to the inability to control the cutting pattern with sufficient accuracy and because the depth of the cut cannot be controlled precisely. The water jet frequency cuts not only the liner material but can cause substantial damage to the wall of the lateral pipe once the jet begins breaking through the liner material.
Accordingly, despite considerable efforts in the development of apparatuses for porting laterals, the commercially available methods rely primarily on the skill of the operator controlling a mechanical cutting device, the quality of his visual reference and the precision by which the cutting device will respond to the operator's remote instructions. Accordingly, it is desirable to provide a method and apparatus for porting laterals in replacement pipe which overcome the deficiencies described above.